Nickel oxide sol-gel ink

ABSTRACT

A method for preparing a nickel oxide precursor ink comprising: preparing a solvent comprising diols and alcohol amines; adding nickel nitrate into the solvent to form a nickel nitrate containing solution; adding at least one metal acetate into the nickel nitrate containing solution to form a nickel nitrate and metal acetate containing solution; adding water to the nickel nitrate and metal acetate containing solution to form a nickel oxide precursor mixture; heating the nickel oxide precursor mixture to 60 to 75 Celsius; and cooling the nickel oxide precursor mixture to form the nickel oxide precursor ink.

RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 17/136,503, filed on Dec. 29, 2020, which is a divisionalapplication of U.S. application Ser. No. 16/577,781, filed on Sep. 20,2019, which claims priority from U.S. Provisional Patent Application No.62/770,389, filed Nov. 21, 2018, the entire disclosures of which areincorporated by reference herein.

TECHNICAL FIELD

Particular embodiments relate generally to compositions for use inphotovoltaic and optoelectronic devices, and more particularly to nickeloxide precursor ink compositions for use as thin film layers inphotovoltaic, electronic, optoelectronic, and mechanical devices.

BACKGROUND

Photovoltaic (PV) and optoelectronic devices comprise multi-layerstructures. Conventional precursor ink formulations for nickel oxidethin films among multiple layers in the PV devices have yieldedincomplete surface coverage, poor surface morphology and undesirableoptoelectronic properties. In perovskite photovoltaics, incompletesurface coverage can lead to increased non-radiative recombination andreduced open-circuit voltage. Poor surface morphology can negativelyimpact the perovskite film growth and quality.

Nickel oxide has been known to serve as a hole-transport and/orelectron-blocking layer in PV and optoelectronic devices. Previousdemonstrations of nickel oxide precursor inks often resulted inincomplete surface coverage, poor film morphology, and/or undesirableoptoelectronic properties.

SUMMARY

To address the foregoing problems with existing solutions, disclosed isa nickel oxide (NiO) precursor ink.

According to some embodiments, a composition for use in a preparation ofa nickel oxide layer includes nickel nitrate (Ni(NO₃)₂·nH₂O, wherein nis 0, 4, 6 or 9), at least one metal acetate; and a solvent combinationcomprising a diol, an alcohol amine, and water.

In particular embodiments, the at least one metal acetate is selectedfrom the group of: nickel acetate tetrahydrate, copper acetatemonohydrate, and combinations thereof.

In particular embodiments, the solvent combination comprises ethyleneglycol, ethanolamine, and water.

In particular embodiments, the solvent combination comprises ethyleneglycol, ethanolamine, water and acetylacetone.

In particular embodiments, the at least one metal acetate comprisesnickel acetate tetrahydrate.

In particular embodiments, wherein the at least one metal acetatecomprises copper acetate monohydrate.

In particular embodiments, the at least one metal acetate comprisesnickel acetate tetrahydrate and copper acetate monohydrate.

According to some embodiments, a method for preparing a nickel oxideprecursor ink includes: first, preparing a solvent comprising diols andalcohol amines. Next, adding nickel nitrate into the solvent to form anickel nitrate containing solution. Next, adding at least one metalacetate into the nickel nitrate containing solution to form a nickelnitrate and metal acetate containing solution.

Next, adding water to the nickel nitrate and metal acetate containingsolution to form a nickel oxide precursor mixture. Next, heating thenickel oxide precursor mixture to 60 to 75 Celsius. Finally, cooling thenickel oxide precursor mixture to form the nickel oxide precursor ink.

In particular embodiments, the nickel nitrate is Ni(NO₃)₂·nH₂O and n is0, 4, 6 or 9.

In particular embodiments, the metal acetate is Ni(CH₃CO₂)₂·xH₂O, and xis 0, 2 or 4.

In particular embodiments, the nickel nitrate is Ni(NO₃)₂·6H₂O and theat least one metal acetate is Ni(CH₃CO₂)₂·4H₂O.

In particular embodiments, the at least one metal acetate comprisesNi(CH₃CO₂)₂·xH₂O and Cu(CH₃CO₂)₂·bH₂O, wherein x is 0, 2 or 4 and b is 0or 1.

In particular embodiments, the nickel nitrate is Ni(NO₃)₂·6H₂O and theat least one metal acetate comprises Ni(CH₃CO₂)₂·4H₂O andCu(CH₃CO₂)₂·1H₂O.

In particular embodiments, the nickel oxide precursor mixture has aconcentration of Ni(NO₃)₂·6H₂O is between 0.7 M and 0.8 M and aconcentration of Ni(CH₃CO₂)₂·4H₂O is between 50 mM and 110 mM.

In particular embodiments, the concentration of Ni(NO₃)₂·6H₂O is 0.72 Mand the concentration of Ni(CH₃CO₂)₂·4H₂O is 103 mM.

In particular embodiments, the nickel oxide precursor mixture has aconcentration of Ni(NO₃)₂·6H₂O between 0.7 M and 0.8 M, a concentrationof Ni(CH₃CO₂)₂·4H₂O between 50 mM and 110 mM, and a concentration ofCu(CH₃CO₂)₂·1H₂O between 20 mM and 41.3 mM.

In particular embodiments, the solvent comprises ethylene glycol andethanolamine.

In particular embodiments, the solvent comprises ethylene glycol andethanolamine; and the ethylene glycol, ethanolamine and water have avolume ratio of 12:1.46:1, respectively.

In particular embodiments, the method is performed under an inertatmosphere having less than 5 ppm water and less than 5 ppm oxygen.

According to some embodiments, a method for depositing a nickel oxidelayer includes: first, preparing a substrate. Next, depositing a nickeloxide precursor ink onto the substrate. The nickel oxide precursor inkincludes a solvent comprising diols, alcohol amines, and water,Ni(NO₃)₂·6H₂O, and at least one metal acetate selected from the groupconsisting of Ni(CH₃CO₂)₂·4H₂O and Cu(CH₃CO₂)₂·1H₂O. Next, annealing thenickel oxide precursor ink at a temperature between 250° to 400° Celsiusfor between 10 minutes and 6 hours. Finally, cooling the nickel oxideprecursor ink to form the nickel oxide layer.

In particular embodiments, the method further includes filtering thenickel oxide precursor ink prior to depositing the nickel oxideprecursor ink onto the substrate.

In particular embodiments, the solvent comprises ethylene glycol,ethanolamine and water.

In particular embodiments, the substrate is selected from the groupconsisting of glass, p-doped silicon, n-doped silicon, sapphire,magnesium oxide, mica, polymers, ceramics, fabrics, wood, drywall,metal, or combinations thereof, and any of the forgoing materials coatedwith materials selected from the group consisting of indium-doped tinoxide (ITO), fluorine-doped tin oxide (FTO), cadmium oxide (CdO), zincindium tin oxide (ZITO), aluminum zinc oxide (AZO), aluminum (Al), gold(Au), calcium (Ca), magnesium (Mg), titanium (Ti), iron (Fe), chromium(Cr), copper (Cu), silver (Ag), nickel (Ni), tungsten (W), molybdenum(Mo), carbon allotropes, or combinations thereof.

In particular embodiments, the method is performed under an environmenthaving a humidity between 10% and 50% and a temperature between 20° and60° Celsius.

In particular embodiments, annealing takes place at a temperature of310° Celsius for a time period of two hours.

According to certain embodiments, a composition for use in a preparationof a nickel oxide layer includes at least one metal nitrate, at leastone metal acetate, and a solvent combination comprising a diol, analcohol amine, and water.

In particular embodiments, the least one metal nitrate comprises coppernitrate, the at least one metal acetate comprises nickel acetate; thesolvent comprises ethylene glycol, ethanolamine, and water.

In particular embodiments, wherein the least one metal nitrate comprisesnickel nitrate, the at least one metal acetate comprises copper acetate,and the solvent comprises ethylene glycol, ethanolamine, and water.

In particular embodiments, wherein the least one metal nitrate comprisesnickel nitrate, the at least one metal acetate comprises nickel acetate,and the solvent comprises ethylene glycol, ethanolamine, and water.

In particular embodiments, wherein: the least one metal nitratecomprises nickel nitrate, the at least one metal acetate comprisesnickel acetate and copper acetate, and the solvent comprises ethyleneglycol, ethanolamine, and water.

Nickel oxide precursor inks disclosed herein may be deposited viasolution-based inks or physical deposition methods, such as spincoating, blade coating, and slot-die coating. Nickel oxide precursorinks disclosed herein also provide tunability through the inkformulation and additive engineering. Solution-based nickel oxideprecursor inks disclosed herein enable high-throughput, low-costdeposition techniques. In addition, increasing the transparency of thelayer/film prepared from nickel oxide precursor inks disclosed hereincan reduce parasitic absorption and increase the short-circuit current.Alternatively, increasing the absorption of higher energy photons may beused as filtering for UV-induced degradation. The formulation of nickeloxide precursor inks disclosed herein provides the optionality fordifferent applications.

The features and advantages of the present disclosure will be readilyapparent to those skilled in the art. While numerous changes may be madeby those skilled in the art, such changes are within the spirit of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example diagram illustrating components of an exemplar PVdevice according to some embodiments of the present disclosure.

FIG. 2 is another example diagram illustrating components of an exemplarPV device according to some embodiments of the present disclosure.

FIG. 3 is a stylized diagram illustrating components of an exemplar PVdevice according to some embodiments of the present disclosure.

FIG. 4 is another stylized diagram illustrating components of anexemplar PV device according to some embodiments of the presentdisclosure.

FIG. 5 is another stylized diagram illustrating components of anexemplar PV device according to some embodiments of the presentdisclosure.

FIG. 6 illustrates SEM (scanning electron microscope) photos of anexample NiO layer from the prior art.

FIG. 7A illustrates an SEM photo of an example NiO layer, taken at20,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 7B illustrates an SEM photo of an example NiO layer, taken at50,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 7C illustrates SEM photos of an example NiO layer, taken at200,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 8A illustrates an SEM photo of another example NiO layer, taken at5,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 8B illustrates an SEM photo of another example NiO layer, taken at20,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 8C illustrates an SEM photo of another example NiO layer, taken at50,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 8D illustrates an SEM photo of another example NiO layer, taken at200,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 8E illustrates SEM photos of another example NiO layer, taken at150,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 9A illustrates an SEM photo of another example NiO layer, taken at20,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 9B illustrates an SEM photo of another example NiO layer, taken at50,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 9C illustrates an SEM photo of another example NiO layer, taken at150,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 10A illustrates an SEM photo of another example NiO layer, taken at20,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 10B illustrates an SEM photo of another example NiO layer, taken at50,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 10C illustrates an SEM photo of another example NiO layer, taken at150,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 11A illustrates an SEM photo of yet another example NiO layer,taken at 20,000× magnification, according to some embodiments of thepresent disclosure.

FIG. 11B illustrates an SEM photo of another example NiO layer, taken at50,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 11C illustrates an SEM photo of another example NiO layer, taken at150,000× magnification, according to some embodiments of the presentdisclosure.

FIG. 12 is an UV-Visible absorptance diagram of NiO and perovskite onNiO layers according to some embodiments of the present disclosure.

FIG. 13 is a photoluminescence diagram of perovskite on NiO layersaccording to some embodiments of the present disclosure.

FIG. 14 is Fourier-transform infrared spectroscopy of NiO layersaccording to some embodiments of the present disclosure.

FIG. 15 is an example film stack including NiO layer according to someembodiments of the present disclosure.

FIG. 16 is another example film stack including NiO layer according tosome embodiments of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present disclosure relates generally to materials to form a thinfilm layer, methods of preparing and applying the materials to thin filmlayer, and apparatus of use of thin film layer in optical devices,electronic devices, mechanical devices, and photovoltaic cells inincreasing short-circuit current and open-circuit voltage, and reducingparasitic absorption. More specifically, this disclosure relates toformation of nickel oxide (NiO) precursor ink compositions, as well asapparatus, methods of use, and preparation of such compositions ofmatter.

The NiO precursor ink of the present disclosure includes a nickelnitrate and/or nickel acetate and may include a metal nitrate or metalacetate dissolved in a solvent mixture comprising a diol, water, and analcohol-amine. In some embodiments the NiO precursor ink includes nickelnitrate an one or more metal acetates dissolved in a solvent mixturecomprising a diol, water, and an alcohol. In other embodiments, the NiOprecursor ink includes nickel acetate and one or more metal nitrates,and does not include nickel nitrate, dissolved in a solvent mixturecomprising a diol, water, and an alcohol-amine. After the NiO precursorink layer has been deposited on a substrate, the layers and/or films maybe heated and annealed, resulting in a combustion reaction that yields anickel oxide thin layer/film which is formed by the NiO precursor inkdisclosed in the present disclosure. The yielded nickel oxide thinlayer/film may serve as an effective hole-transport layer inphotovoltaic devices.

In some embodiments, the NiO precursor ink of the present disclosure mayinclude other metals as described herein. These metals may act asdopants in the resulting nickel oxide thin film, resulting inhole-transporting or electron-transporting nickel oxide thin films,depending on the metal dopant(s) included in the NiO precursor ink.

Examples of compounds to prepare the NiO precursor ink may include, butare not limited to, anhydrous nickel nitrate, nickel nitratehexahydrate, nickel nitrate nonahydrate, nickel nitrate tetrahydrate,nickel nitrate dihydrate, and any derivative hydrates of nickel nitrate,and anhydrous nickel acetate, nickel acetate dihydrate, nickel acetatetetrahydrate, and anhydrous copper nitrate, copper nitrate monohydrate,copper nitrate sesquihydrate, copper nitrate hemipentahydrate, coppernitrate trihydrate, copper nitrate hexahydrate, and any derivativehydrates of copper nitrate, and anhydrous copper acetate, copper acetatemonohydrate.

The NiO precursor inks of the present disclosure may be formulated usinga mixture of nickel nitrate (Ni(NO₃)₂), a metal acetate, and water in adiol solvent with an alcohol-amine additive. In certain embodiments, themetal acetate may be one or more of nickel acetate (Ni(CH₃CO₂)₂) orcopper acetate (Cu(CH₃CO₂)₂), and amines, diamines, and acetylacetone(and derivatives thereof) may also be included in the NiO precursor ink.Compositions and methods for forming embodiments of the NiO precursorink are described further herein. After the NiO precursor ink isformulated, it may be deposited and annealed to form a NiO thin film.The resulting NiO thin film may be a p-type semiconductor. In someembodiments, the NiO precursor ink may be applied to form an NiO thinfilm in a variety of electronic devices, including but not limited tophotovoltaics (PV), field effect transistors (FETs), light emittingdiodes (LEDs), charge coupled devices (CCDs), photodiodes, x-raydetectors, and complementary metal-oxide-semiconductors (CMOS).

In some embodiments, a nickel oxide precursor ink may be formulated witha mixture of nickel nitrate, nickel acetate, water, and ethanol amine inan ethylene glycol solvent. In other embodiments, a nickel oxideprecursor ink may be formulated with a mixture of nickel nitrate, nickelacetate, water, ethanol amine, and acetylacetone in an ethylene glycolsolvent. In yet other embodiments, a nickel oxide precursor ink may beformulated with a mixture of nickel nitrate, copper acetate, water, andethanol amine in an ethylene glycol solvent. In yet other embodiments, anickel oxide precursor ink may be formulated with a mixture of nickelnitrate, copper acetate, water, ethanol amine, and acetylacetone in anethylene glycol solvent. In other embodiments, a nickel oxide precursorink may be formulated with a mixture of nickel nitrate, a metal acetatehaving the formula M(CH₃CO₂)_(y) wherein M may be any metal (forexample, Cu, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf,V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Pd, Pt, Cu, Ag,Au, Zn, Cd, Hg, B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Se, Te,La, Ce, Pr, Nd, Sm, Er, Gd, Tb, Dy, Ho, Er, Ym, Yb, Lu, Ac, Th, Pa, andU) and y corresponds to the oxidation state of the metal M (e.g., y=2where M is Cu²⁺ and y=6 where M is W⁶⁺), water, and ethanol amine in anethylene glycol solvent.

In some embodiments, hydrates of nickel nitrate (e.g., Ni(NO₃)₂·aH₂O),nickel acetate (e.g., Ni(CH₃CO₂)₂·bH₂O), copper acetate (e.g.,Cu(CH₃CO₂)₂·cH₂O), or metal acetate (e.g., M(CH₃CO₂)_(y)·dH₂O) may beincluded in the nickel oxide precursor ink formulation as describedherein, where a, b, c, and d in the forgoing formulas correspond to anumber of H₂O molecules in the hydrate.

In some embodiments, compounds for preparing the NiO precursor inks mayinclude nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O), nickel acetatetetrahydrate (Ni(CH₃CO₂)₂·4H₂O), copper nitrate trihydrate(Cu(NO₃)₂·3H₂O), and copper acetate monohydrate (Cu(CH₃CO₂)₂·H₂O).

Examples of solvents for preparing the NiO precursor ink may include,but are not limited to, one or more of glycerol; ethylene glycol;propylene glycol; methanol; ethanol; and any other compounds comprisingat least one hydroxyl groups, such as alcohols and diols; ammonia;acetone; acetylacetone, and any compounds comprising at least onecarbonyl group; ethylamine, and any other aryl and alkylamines;ethanolamine, and any amines comprising at least one hydroxyl group;water; di- and polyamines, and any other solvent suitable to dissolvethe compounds for preparing the NiO precursor ink.

In certain embodiments, a solvent for preparing the NiO precursor inksmay comprise ethylene glycol, ethanolamine and water. In one particularembodiment, the solvent may comprise ethylene glycol, ethanolamine andwater in a ratio of 12:1.46:1 by volume.

In a particular embodiment, the NiO precursor ink consists of Ni(NO₃)₂and Ni(CH₃CO₂)₂ dissolved in a solvent mixture consisting of a diol, analcohol amine, and water.

In another embodiment, the NiO precursor ink consists of Ni(NO₃)₂ and ametal acetate (M(CH₃CO₂)_(y)) dissolved in a solvent mixture consistingof a diol, an alcohol amine, and water.

In another embodiment, the NiO precursor ink consists of Ni(NO₃)₂,Ni(CH₃CO₂)₂ and a metal acetate (M(CH₃CO₂)_(y)) dissolved in a solventmixture consisting of a diol, an alcohol amine, and water.

In another embodiment, the NiO precursor ink consists of Ni(NO₃)₂,Ni(CH₃CO₂)₂ and a metal nitrate (M(NO₃)_(y)) dissolved in a solventmixture consisting of a diol, an alcohol amine, and water.

In another embodiment, the NiO precursor ink consists of Ni(CH₃CO₂)₂,and a metal nitrate (M(NO₃)_(y)) dissolved in a solvent mixtureconsisting of a diol, an alcohol amine, and water.

An example preparation of the NiO precursor ink may comprise 0.7-0.8 Mnickel nitrate hexahydrate and 50-110 mM nickel acetate tetrahydrate ina solvent which comprises ethylene glycol, ethanolamine and water in avolume ratio of 5-20 to 1-5 to 1-5, respectively. In a particularembodiment, the preparation of the NiO precursor ink may comprise 0.72 Mnickel nitrate hexahydrate and 103 mM nickel acetate tetrahydrate in asolvent which comprises ethylene glycol, ethanolamine and water in avolume ratio of 12:1.46:1. In some embodiments, the NiO precursor inkmay additionally include 0-20 mol % copper and 0-50 mol % acetate.

Another example preparation of the NiO precursor ink may comprise0.7-0.8 M nickel nitrate and 50-110 mM metal acetate in a solvent whichcomprises ethylene glycol, ethanolamine and water in a volume ratio of5-20 to 1-5 to 1-5, respectively. In a particular embodiment, thepreparation of the NiO precursor ink may comprise 0.72 M nickel nitratehexahydrate and 103 mM metal acetate in a solvent which comprisesethylene glycol, ethanolamine and water in a volume ratio of 12:1.46:1.In some embodiments, the NiO precursor ink may additionally include 0-20mol % copper and 0-50 mol % acetate.

Another example preparation of the NiO precursor ink may comprise0.7-0.8 M nickel nitrate hexahydrate, 50-110 mM nickel acetatetetrahydrate, and 20-41.3 mM metal nitrate in a solvent which comprisesethylene glycol, ethanolamine and water in a volume ratio of 5-20 to 1-5to 1-5, respectively. In a particular embodiment, the metal nitrate maybe copper nitrate trihydrate. In a particular embodiment, thepreparation of the NiO precursor ink may comprise 0.72 M nickel nitratehexahydrate, 103 mM nickel acetate tetrahydrate, and 30 mM metal nitratein a solvent which comprises ethylene glycol, ethanolamine and water ina volume ratio of 12:1.46:1.

Another example preparation of the NiO precursor ink may comprise0.7-0.8 M nickel nitrate hexahydrate, 50-110 mM nickel acetatetetrahydrate, and 20-41.3 mM metal acetate in a solvent which comprisesethylene glycol, ethanolamine and water in a volume ratio of 5-20 to 1-5to 1-5, respectively. In some embodiments, the metal nitrate may becopper acetate. In a particular embodiment, the preparation of the NiOprecursor ink may comprise 0.72 M nickel nitrate hexahydrate, 103 mMnickel acetate tetrahydrate, and 30 mM metal acetate in a solvent whichcomprises ethylene glycol, ethanolamine and water in a volume ratio of12:1.46:1.

Another example preparation of the NiO precursor ink may comprise0.7-0.8 M metal nitrate and 50-110 mM nickel acetate tetrahydrate in asolvent which comprises ethylene glycol, ethanolamine and water in avolume ratio of 5-20 to 1-5 to 1-5, respectively. In a particularembodiment, the preparation of the NiO precursor ink may comprise 0.72 Mmetal nitrate and 103 mM nickel acetate tetrahydrate in a solvent whichcomprises ethylene glycol, ethanolamine and water in a volume ratio of12:1.46:1.

An example method for preparing the NiO may include, but is not limitedto, the following steps. First, a solvent is prepared comprising diolsand amines which comprise at least one hydroxyl group (an“alcohol-amine”). For example, the solvent may be prepared by mixingethanolamine into ethylene glycol. Next, Ni(NO₃)₂·aH₂O is added to thesolvent, where a may be 0, 4, 6 or 9. In particular embodiments, thenickel nitrate may be nickel nitrate hexahydrate (a=6). Next,Ni(CH₃CO₂)₂·bH₂O is added to the mixture, where b may be 0, 2, or 4. Thenickel acetate may be nickel acetate tetrahydrate, in particularembodiments. Next, water is added to the mixture. Next, the mixture isheated. Finally, the mixture is cooled to form the NiO precursor ink. Incertain embodiments, when each component is added to the mixture, themixture may be mixed by vibrating, agitating, stirring, homogenizing,combining turbulent flows, vortex mixing, or any other known method ofmixing. In certain embodiments, the NiO layer may be prepared in eitheran inert atmosphere or an atmosphere having a high humidity (e.g.greater than 4 grams H₂O per liter of the atmosphere).

In some embodiments, water may be added before the cooling step, so thatthe final concentration of nickel nitrate hexahydrate is 0.7-0.8 M andthe final concentration of nickel acetate tetrahydrate is 50-110 mM.

The NiO precursor ink may be deposited onto a variety of substrates toform a thin film NiO layer for use in optical, mechanical, andelectronic applications, including but not limited to photovoltaics(PV), field effect transistors (FETs), light emitting diodes (LEDs),charge coupled devices (CCDs), photodiodes, x-ray detectors, andcomplementary metal-oxide-semiconductors (CMOS). In some embodiments,the layer formed by the NiO precursor ink may be used in photovoltaiccells. In particular embodiments, the layer formed by the NiO precursorink may be used as hole-transport and/or electron-transport layers. Incertain embodiments, the NiO precursor ink maybe deposited as athin-film IFL. In particular embodiments, the NiO precursor ink may bedeposited to form a thin film NiO layer in a photovoltaic device with aperovskite photoactive layer.

Suitable substrate materials include any one or more of: glass; quartz,p-doped silicon substrate; n-doped silicon substrate; sapphire;magnesium oxide (MgO); mica; polymers (e.g., PET, PEG, PES,polypropylene, polyethylene, etc.); ceramics; fabrics (e.g., cotton,silk, wool); wood; drywall; metal; and combinations thereof. In someembodiments, the substrate onto which the NiO precursor ink may bedeposited may be coated with an electrode. The electrode may be eitheran anode or a cathode. Suitable materials for the electrode may includeindium-doped tin oxide (ITO); fluorine-doped tin oxide (FTO); cadmiumoxide (CdO); zinc indium tin oxide (ZITO); aluminum zinc oxide (AZO);aluminum (Al); gold (Au); calcium (Ca); magnesium (Mg); titanium (Ti);iron (Fe); chromium (Cr); copper (Cu); silver (Ag); nickel (Ni);tungsten (W); molybdenum (Mo); carbon (and allotropes thereof); andcombinations thereof, and any other materials which may function as anelectrode. For example, the substrate with electrode coating may includeITO-coated glass, FTO-coated glass, Ag-coated glass, CdO-coated glass,and ITO-coated PET.

In some embodiments the substrate may be additionally coated with one ormore interfacial layers (IFL) as described herein. In some embodiments,the IFL may be alumina (Al₂O₃). In some embodiments, the IFL may form acontiguous layer. In other embodiments, the IFL may form anon-contiguous layer.

An example method for depositing the NiO precursor ink may include, butis not limited to, preparing a substrate, depositing the NiO precursorink onto the substrate, annealing the NiO precursor ink and cooling theNiO precursor ink to form a thin film NiO layer. Depositing the NiOprecursor ink onto the substrate may include depositing the NiOprecursor ink onto any preceding layers deposited onto the substrate.For example, an electrode layer may be deposited onto the substrateprior to deposition of the NiO precursor ink, which may then bedeposited onto the electrode layer. Likewise, in some embodiments, anelectrode layer and one or more interfacial layers may be deposited ontothe substrate prior to deposition of the NiO precursor ink.

In some embodiments, depositing the NiO precursor ink may be performedby spin coating, blade coating, slot-die coating, screen printing,roll-to-roll coating, spray coating, dip coating, or gravure printing.In some embodiments, the NiO precursor ink may be deposited onto thesubstrate in an environment having a relative humidity between 10 and50% and a temperature between 20° and 60° Celsius. In a particularembodiment, the NiO precursor ink may be deposited onto the substrate inan environment having a relative humidity of 35% and a temperature of35° Celsius. In some embodiments, the NiO precursor ink may be filteredbefore being deposited onto the substrate. In particular embodiments,filtering the NiO precursor ink may include dispensing the NiO precursorink through 0.2 μm filter. In some embodiments, annealing may take placeat a temperature between 250° Celsius and 400° Celsius for a time periodbetween 30 minutes and 6 hours. In a particular embodiment, annealingmay take place at a temperature of 310° Celsius for a time period of twohours. In some embodiments, the step of annealing the IFL on thesubstrate may include increasing the temperature from 35° to 310°Celsius at a rate of approximately 50° Celsius per five minutes. Coolingthe NiO thin film layer formed after annealing the NiO precursor ink mayinclude cooling it to near-room temperature (20°-50° Celsius) byallowing the substrate and thin film layers to rest in a near-roomtemperature environment. In some embodiments, the NiO thin film layermay annealed one or more times after the first annealing step, in thesame manner as described above. For example, a substrate with an NiOthin film layer deposited as disclosed herein may be stored andreannealed prior to subsequent processing steps.

In a particular embodiment, the method for depositing the NiO precursorink may include preparing a substrate, depositing an alumina thin filmlayer, depositing the NiO precursor ink onto the alumina thin film,annealing the NiO precursor ink to form a NiO thin film, depositing aperovskite material, depositing an interfacial layer, and depositing anelectrode. In some embodiments, depositing the NiO precursor ink mayfollow a pattern which starts at one side of the substrate and coversthe substrate row by row continuously to ensure a good coverage of NiOprecursor ink on the substrate without dripping.

FIG. 1 illustrates a stylized diagram of a perovskite material device1000 according to some embodiments. Although various components of thedevice 1000 are illustrated as discrete layers comprising contiguousmaterial, it should be understood that FIG. 1 is a stylized diagram;thus, embodiments in accordance with it may include such discretelayers, and/or substantially intermixed, non-contiguous layers,consistent with the usage of “layers” previously discussed herein. Thedevice 1000 includes first and second substrates 1010 and 1070. A firstelectrode 1020 is disposed upon an inner surface of the first substrate1010, and a second electrode 1060 is disposed on an inner surface of thesecond substrate 1070. An active layer 1100 is sandwiched between thetwo electrodes 1020 and 1060. The active layer 1100 includes aninterfacial layer (IFL) 1030; photoactive material (PAM) layer 1040; andan IFL 1050.

A perovskite material device according to some embodiments mayoptionally include one or more substrates. In some embodiments, eitheror both of the first and second electrodes 1020 and 1060 may be coatedor otherwise disposed upon a substrate, such that the electrode isdisposed substantially between a substrate and the active layer. Thematerials of composition of devices (e.g., substrate, electrode, activelayer and/or active layer components) may in whole or in part be eitherrigid or flexible in various embodiments. In some embodiments, anelectrode may act as a substrate, thereby negating the need for aseparate substrate.

A substrate, such as either or both of first and second substrates 1010and 1070, may be flexible or rigid. If two substrates are included, atleast one should be transparent or translucent to electromagnetic (EM)radiation (such as, e.g., UV, visible, or IR radiation). If onesubstrate is included, it may be similarly transparent or translucent,although it need not be, so long as a portion of the device permits EMradiation to contact the active layer 1100.

As previously noted, an electrode (e.g., one of electrodes 1020 and 1060of FIG. 1 ) may be either an anode or a cathode. In some embodiments,one electrode may function as a cathode, and the other may function asan anode. Either or both electrodes 1020 and 1060 may be coupled toleads, cables, wires, or other means enabling charge transport to and/orfrom the device 1000. An electrode may constitute any conductivematerial, and at least one electrode should be transparent ortranslucent to EM radiation, and/or be arranged in a manner that allowsEM radiation to contact at least a portion of the active layer 1100.

The example NiO precursor inks described herein may be deposited by anyof the methods described herein to form a NiO thin film layer as aninterfacial layer (IFL) or in addition to other IFLs as described below.An interfacial layer may include any suitable material for enhancingcharge transport and/or collection between adjacent layers or materials;it may also help prevent or reduce the likelihood of chargerecombination once a charge has been transported away from one of thematerials adjacent to the interfacial layer. An interfacial layer mayadditionally physically and electrically homogenize its substrates tocreate or reduce variations in substrate roughness, dielectric constant,adhesion, creation or quenching of defects (e.g., charge traps, surfacestates). Suitable interfacial materials may include any one or more of:Ag; Al; Au; B; Bi; Ca; Cd; Ce; Co; Cr; Cu; Fe; Ga; Ge; H; In; Mg; Mn;Mo; Nb; Ni; Pt; Sb; Sc; Si; Sn; Ta; Ti; V; W; Y; Zn; Zr; carbides of anyof the foregoing metals (e.g., SiC, Fe₃C, WC, VC, MoC, NbC); silicidesof any of the foregoing metals (e.g., Mg₂Si, SrSi₂, Sn₂Si); oxides ofany of the foregoing metals (e.g., alumina, silica, titania, SnO₂, ZnO,WO₃, V₂O₅, MoO₃, NiO, ZrO₂, HfO₂), include transparent conducting oxides(“TCOs”) such as indium tin oxide, aluminum doped zinc oxide (AZO),cadmium oxide (CdO), and fluorine doped tin oxide (FTO); sulfides of anyof the foregoing metals (e.g., CdS, MoS₂, SnS₂); nitrides of any of theforegoing metals (e.g., GaN, Mg₃N₂, TiN, BN, Si₃N₄); selenides of any ofthe foregoing metals (e.g., CdSe, FeS₂, ZnSe); tellurides of any of theforegoing metals (e.g., CdTe, TiTe₂, ZnTe); phosphides of any of theforegoing metals (e.g., InP, GaP, GaInP); arsenides of any of theforegoing metals (e.g., CoAs₃, GaAs, InGaAs, NiAs); antimonides of anyof the foregoing metals (e.g., AlSb, GaSb, InSb); halides of any of theforegoing metals (e.g., CuCl, CuI, Bib); pseudohalides of any of theforegoing metals (e.g., CuSCN, AuCN, Fe(SCN)₂); carbonates of any of theforegoing metals (e.g., CaCO₃, Ce₂(CO₃)₃); functionalized ornon-functionalized alkyl silyl groups; graphite; graphene; fullerenes;carbon nanotubes; any mesoporous material and/or interfacial materialdiscussed elsewhere herein; and combinations thereof (including, in someembodiments, bilayers, trilayers, or multi-layers of combinedmaterials). In some embodiments, an interfacial layer may includeperovskite material. Further, interfacial layers may comprise dopedembodiments of any interfacial material mentioned herein (e.g., Y-dopedZnO, N-doped single-wall carbon nanotubes). Interfacial layers may alsocomprise a compound having three of the above materials (e.g., CuTiO₃,Zn₂SnO₄) or a compound having four of the above materials (e.g.,CoNiZnO). The materials listed above may be present in a planar,mesoporous or otherwise nano-structured form (e.g. rods, spheres,flowers, pyramids), or aerogel structure.

In certain embodiments, an alumina IFL layer as described herein may bedeposited according to the following method. First an alumina precursorsolution may be prepared. The alumina precursor solution may be preparedby dissolving aluminum nitrate in a mixture of butanol, chloroform, andmethanol. In some embodiments the butanol, chloroform, and methanolsolution may have a ratio of 1:1:1 by volume of butanol, chloroform, andmethanol. In certain embodiments, aluminum nitrate may be dissolved inwith butanol, chloroform, and methanol to form a solution having aconcentration of 25 mM of aluminum nitrate.

Next, the alumina precursor solution may be deposited onto a substrate.Depositing the alumina precursor solution onto the substrate may includedepositing the alumina precursor solution precursor ink onto anypreceding layers deposited onto the substrate. In some embodiments, thealumina precursor solution may be deposited by spin coating, slot diecoating, or blade coating, amongst others described herein. Inparticular embodiments, the alumina precursor solution may be depositedso as to result in a layer 1 nm to 100 nm in thickness. In anotherembodiment, the alumina precursor solution may be deposited at athickness of less than 1 nm. In some embodiments, the alumina precursorsolution may be deposited in a continuous manner over the entire area ofthe substrate. In other embodiments, the alumina precursor solution maybe deposited in a discontinuous manner such that the alumina precursorsolution covers portions of the area of the substrate. After deposition,the alumina precursor may be annealed. To anneal the alumina precursor,the temperature of the substrate may be increased to 310° Celsius over a25-minute interval, and then held at 310° Celsius for 35 minutes.Annealing the alumina precursor may occur in a controlled humidityenvironment. In some embodiments, the controlled humidity environmentmay be controlled to maintain a humidity of 25% relative humidity duringdeposition and annealing of the alumina oxide precursor. Afterannealing, the substrate may be allowed to cool to room temperature inambient conditions. After annealing and cooling, the alumina precursorto form an alumina layer, subsequent layers may be deposited onto thealumina layer, such as an NiO layer by the methods described herein. Thealumina layer may be continuous or discontinuous over the surface of thesubstrate.

Although referred to herein as NiO and/or nickel oxide, it should benoted that various ratios of nickel and oxygen may be used in formingnickel oxide. Thus, although some embodiments discussed herein aredescribed with reference to NiO, such description is not intended todefine a required ratio of nickel in oxygen. Rather, embodiments mayinclude any one or more nickel-oxide compounds, each having an nickeloxide ratio according to Ni_(x)O_(y), where x may be any value, integeror non-integer, between approximately 1 and 100. In some embodiments, xmay be between approximately 1 and 3 (and, again, need not be aninteger). Likewise, y may be any value, integer or non-integer, between0.1 and 100. In some embodiments, y may be between 2 and 4 (and, again,need not be an integer). In addition, various crystalline forms ofNi_(x)O_(y) may be present in various embodiments, such as alpha, gamma,and/or amorphous forms.

Furthermore, although referred to herein as Al₂O₃ and/or alumina, itshould be noted that various ratios of aluminum and oxygen may be usedin forming alumina. Thus, although some embodiments discussed herein aredescribed with reference to Al₂O₃, such description is not intended todefine a required ratio of aluminum in oxygen. Rather, embodiments mayinclude any one or more aluminum-oxide compounds, each having analuminum oxide ratio according to Al_(x)O_(y), where x may be any value,integer or non-integer, between approximately 1 and 100. In someembodiments, x may be between approximately 1 and 3 (and, again, neednot be an integer). Likewise, y may be any value, integer ornon-integer, between 0.1 and 100. In some embodiments, y may be between2 and 4 (and, again, need not be an integer). In addition, variouscrystalline forms of Al_(x)O_(y) may be present in various embodiments,such as alpha, gamma, and/or amorphous forms of alumina.

Additionally, any metal oxide referred to herein may have various ratiosof metal and oxygen. Embodiments may include any one or more metal-oxidecompounds, each having an metal oxide ratio according to M_(x)O_(y),where x may be any value, integer or non-integer, between approximately1 and 100. In some embodiments, x may be between approximately 1 and 3(and, again, need not be an integer). Likewise, y may be any value,integer or non-integer, between 0.1 and 100. In some embodiments, y maybe between 2 and 4 (and, again, need not be an integer). In addition,various crystalline forms of M_(x)O_(y) may be present in variousembodiments, such as alpha, gamma, and/or amorphous forms of alumina.

Any interfacial material discussed herein may further comprise dopedcompositions. To modify the characteristics (e.g., electrical, optical,mechanical) of an interfacial material, a stoichiometric ornon-stoichiometric material may be doped with one or more elements(e.g., Na, Y, Mg, N, P) in amounts ranging from as little as 1 ppb to 50mol %. Some examples of interfacial materials include: NiO, TiO₂,SrTiO₃, Al₂O₃, ZrO₂, WO₃, V₂O₅, MO₃, ZnO, graphene, and carbon black.Examples of possible dopants for these interfacial materials include:Be, Mg, Ca, Sr, Ba, Sc, Y, Nb, Ti, Fe, Co, Ni, Cu, Ga, Sn, In, B, N, P,C, S, As, a halide, a pseudohalide (e.g., cyanide, cyanate, isocyanate,fulminate, thiocyanate, isothiocyanate, azide, tetracarbonylcobaltate,carbamoyldicyanomethanide, dicyanonitrosomethanide, dicyanamide, andtricyanomethanide), and Al in any of its oxidation states. Referencesherein to doped interfacial materials are not intended to limit theratios of component elements in interfacial material compounds.

Photoactive material 1040 may comprise any photoactive compound, such asany one or more of silicon (in some instances, single-crystallinesilicon), cadmium telluride, cadmium sulfide, cadmium selenide, copperindium gallium selenide, gallium arsenide, germanium indium phosphide,one or more semiconducting polymers, and combinations thereof. In someembodiments, photoactive material 1040 may include one or moreperovskite materials. Perovskite materials include compositions havingthe formula CMX₃, where C is a cation, M is a metal cation and X is ananion. In some embodiments, perovskite materials may deviate from thestrict stoichiometry represented as CMX₃ and include bothsubstoichiometric and superstoichiometric compositions. Such perovskitesmay be represented by the formula C_(x)M_(y)X_(Z) where x, y, and z arereal numbers. In some embodiments, solid perovskite-containing materialmay be deposited by any suitable means (e.g., vapor deposition, solutiondeposition, direct placement of solid material, etc.). Devices accordingto various embodiments may include one, two, three, or more photoactivecompounds (e.g., one, two, three, or more perovskite materials). Incertain embodiments, photoactive material 1040 may include MAPbI₃,FAPbI₃, 5-AVA·HCl:FAPbI₃, CHP:FAPbI₃, Cs:FAPbI₃, FA:MA:CsPbI₃·yBr_(y),CsPbI₃, and/or FA:MAPbI₃, where MA is methylammonium, FA isformamidinium, 5-AVA is 5-aminovaleric acid, and CHP isN-cyclohexyl-2-pyrrolidone. Additionally, photoactive material 1040 mayinclude both substoichiometric and superstoichiometric compositions ofthe preceding perovskite materials. In embodiments including multiplephotoactive materials, each of the photoactive materials may beseparated by one or more interfacial layers. For example, FIG. 2illustrates a stylized diagram of a perovskite material device 2000,according to some embodiments. The device 2000 includes first and secondsubstrates 2010 and 2090. A first electrode 2020 is disposed upon aninner surface of the first substrate 2010, and a second electrode 2080is disposed on an inner surface of the second substrate 2070. An activelayer 2100 is sandwiched between the two electrodes 2020 and 2080. Theactive layer 2100 includes an IFL 2030; photoactive materials (PAM)layer 2040; IFL 2050 and 2055; PAM layer 2060 and IFL 1070. In someembodiments PAM layers 2040 and 2060 may be composed of differentphotoactive materials which are photoactive in response to differentwavelengths of light.

Charge transport material (e.g., a charge transport material of chargetransport layer 3050 in FIG. 3 ) may include solid-state chargetransport material (i.e., a colloquially labeled solid-stateelectrolyte), or it may include a liquid electrolyte and/or ionicliquid. Any of the liquid electrolyte, ionic liquid, and solid-statecharge transport material may be referred to as charge transportmaterial. As used herein, “charge transport material” refers to anymaterial, solid, liquid, or otherwise, capable of collecting chargecarriers and/or transporting charge carriers. For instance, in PVdevices according to some embodiments, a charge transport material maybe capable of transporting charge carriers to an electrode. Chargecarriers may include holes (the transport of which could make the chargetransport material just as properly labeled “hole transport material”)and electrons. Holes may be transported toward an anode, and electronstoward a cathode, depending upon placement of the charge transportmaterial in relation to either a cathode or anode in a PV or otherdevice. Suitable examples of charge transport material according to someembodiments may include any one or more of: perovskite material; I⁻/I₃⁻; Co complexes; polythiophenes (e.g., poly(3-hexylthiophene) andderivatives thereof, or P3HT); carbazole-based copolymers such aspolyheptadecanylcarbazole dithienylbenzothiadiazole and derivativesthereof (e.g., PCDTBT); other copolymers such aspolycyclopentadithiophene-benzothiadiazole and derivatives thereof(e.g., PCPDTBT); poly(triaryl amine) compounds and derivatives thereof(e.g., PTAA); Spiro-OMeTAD; fullerenes and/or fullerene derivatives(e.g., C₆₀, PCBM); and combinations thereof. In certain embodiments,charge transport material may include any material, solid or liquid,capable of collecting charge carriers (electrons or holes), and/orcapable of transporting charge carriers. Charge transport material ofsome embodiments therefore may be n- or p-type active and/orsemi-conducting material. Charge transport material may be disposedproximate to one of the electrodes of a device. In certain embodiments,the type of charge transport material may be selected based upon theelectrode to which it is proximate. For example, if the charge transportmaterial collects and/or transports holes, it may be proximate to ananode so as to transport holes to the anode. However, the chargetransport material may instead be placed proximate to a cathode and beselected or constructed so as to transport electrons to the cathode.

In some embodiments, another IFL may be disposed between an IFL and anelectrode such as is illustrated in FIG. 3 described below.

FIG. 3 illustrates another stylized diagram of a perovskite materialdevice 3000 according to some embodiments. The device 3000 includesfirst and second substrates 3010 and 3070. The first electrode 3020 isdisposed upon an inner surface of the first substrate 3010, and a secondelectrode 3060 is disposed on an inner surface of the second substrate3070. An active layer 3100 is sandwiched between the two electrodes 3020and 3060. The active layer 3100 includes a first IFL 3030, and a secondIFL 3035; the photoactive materials (PAM) 3040; and the CTL 3040. Incertain embodiments, the device 3000 may comprise more than one IFL3010.

According to various embodiments, the device 2000 may optionally includean interfacial layer 2030 between any two other layers and/or materials,although the devices 2000 need not contain any interfacial layers. Forexample, a perovskite material device may contain zero, one, two, three,four, five, or more interfacial layers.

As will be apparent to one of ordinary skill in the art with the benefitof this disclosure, various other embodiments are possible, such as adevice with multiple photoactive layers. In some embodiments, asdiscussed above, each photoactive layer may be separated by aninterfacial layer.

FIG. 4 depicts an example device 4000 in accordance with variousembodiments. The device 4000 illustrates embodiments including first andsecond glass substrates 4010 and 4070. A first electrode (ITO) 4020 isdisposed upon an inner surface of the first substrate 4010, and a secondelectrode (Al) 4060 is disposed on an inner surface of the secondsubstrate 4070. An active layer 4100 is sandwiched between the twoelectrodes 4020 and 4060. The active layer 4100 includes an IFL (e.g.,NiO) 4030, a photoactive material (e.g., MAPbI₃, FAPbI₃) 4040, and acharge transport layer 4050.

FIG. 5 depicts another example device 5000 in accordance with variousembodiments. The device 5000 illustrates embodiments including first andsecond glass substrates 5010 and 5080. A first electrode (ITO) 5020 isdisposed upon an inner surface of the first substrate 5010, and a secondelectrode 5070 is disposed on an inner surface of the second substrate5080. Second electrode 5070 may be a chromium-aluminum bilayer (Cr/Al),wherein a layer of chromium is coated with a layer of aluminum to formthe bilayer. An active layer 5100 is sandwiched between the twoelectrodes 5020 and 5070. The active layer 5100 includes an IFL (e.g.,Al₂O₃) 4030, a second IFL (e.g., NiO) 5040, a photoactive material(e.g., MAPbI₃, FAPbI₃) 5050, and a charge transport layer (e.g., Co)5060.

FIG. 6 illustrates SEM photos of an example NiO layer produced bymethods prior to those disclosed herein. The SEM photos are of the sameNiO layer, taken at 10,000× magnification (top) and 100,000×magnification (bottom). The NiO layer shown was produced by theformulation of a NiO precursor solution disclosed in Steirer et al., J.Mater. Chem. A, 2015, 3, 10949, Nickel oxide interlayer films fromnickel formate-ethylenediamine precursor: influence of annealing on thinfilm properties and photovoltaic device performance. The SEM images showthat NiO layers formed by the prior method has poor coverage and anirregular grain structure, indicated by the substantial number of largeand distinct dark and light areas seen in the image. This may lead to(i) defects that cause parasitic absorption losses when the NiO layer isapplied in a photovoltaic device, (ii) incomplete and non-uniformcoverage that causes shunting and/or series resistance losses, and/or(iii) undesirable surface roughness.

FIG. 7A-C illustrates SEM photos of an example NiO layer disclosedherein, in accordance with certain embodiments. The NiO layer formedbased on the method described herein shows a superior film coveragecompared to the NiO layer shown in FIG. 6 . In this embodiment, theformulation of the NiO precursor ink deposited to form the NiO layer maycomprise 0.95 M nickel nitrate hexahydrate and 213 mol % ethanolamine inethylene glycol, where the mole percentage of ethanolamine is relativeto Ni moles. FIG. 7A illustrates an image of the surface of the NiOlayer taken at 20,000× magnification, FIG. 7B illustrates an image ofthe surface of the NiO layer taken at 50,000× magnification, and FIG. 7Cillustrates two images taken of a profile of the NiO layer taken at200,000× magnification. As can be seen from the images the NiO layerproduced by the methods disclosed herein has a much more uniform grainstructure than the NiO layer produced by prior methods illustrated inFIG. 6 , leading to improved coverage and lower parasitic absorptionwhen applied in a photovoltaic device as described herein.

FIGS. 8A-E illustrate SEM photos of another example NiO layer disclosedherein, in accordance with certain embodiments. The NiO layer formedbased on the method described herein shows a superior film coveragecomparing to the NiO layer shown in FIG. 6 , which may result in abetter electronic performance. FIG. 8A illustrates an image of thesurface of the NiO layer taken at 5,000× magnification, FIG. 8Billustrates an image of the surface of the NiO layer taken at 20,000×magnification, FIG. 8C illustrates an image of the surface of the NiOlayer taken at 50,000× magnification, FIG. 8D illustrates an image ofthe surface of the NiO layer taken at 200,000× magnification, and FIG.8E illustrates two images taken of a profile of the NiO layer taken at150,000× magnification. In this embodiment, the formulation of the NiOprecursor ink deposited to form the NiO layer may comprise 0.95 M nickelnitrate hexahydrate, 5 mol % copper acetate monohydrate, 231 mol %ethanolamine, and 488 mol % water in ethylene glycol, where the molepercentage of copper acetate monohydrate, ethanolamine, and water arerelative to Ni moles. As with the images show in FIGS. 7A-C, the NiOlayer pictured in FIGS. 8A-E display a significantly more uniformstructure than those of the NiO layer produced by prior methods picturedin FIG. 6 . For example, in FIG. 8D the grain boundaries, shown as darkareas, are substantially smaller and more regularly spaced when viewedat 200,000× magnification than the grain boundaries, shown as darkareas, in FIG. 6 are when viewed at 100,000× magnification.

FIGS. 9A-C illustrate SEM photos of the example NiO layer as describedherein having 5 mol % Cu and 5 mol % acetate in the NiO precursor inkused to form the NiO layer. FIGS. 9A-C show profile images of the NiOlayer disposed in a photovoltaic device, as captured at 20,000×, 50,000×and 150,000× magnification, respectively. The NiO layer can be seen inthe images as a “band” running across the center of each image.

FIGS. 10A-C illustrate SEM photos of another example NiO layer asdescribed herein having 5 mol % Cu and 12.5 mol % acetate in the NiOprecursor ink used to form the NiO layer. FIGS. 10A-C show profileimages of the NiO layer disposed in a photovoltaic device, as capturedat 20,000×, 50,000× and 150,000× magnification, respectively. The NiOlayer can be seen in the images as a “band” running across the center ofeach image.

FIGS. 11A-C illustrate SEM photos of yet another example NiO layer, inaccordance with certain embodiments. FIGS. 10A-C show profile images ofthe NiO layer disposed in a photovoltaic device, as captured at 20,000×,50,000× and 150,000× magnification, respectively. The illustrated NiOlayer formed based on the method described herein shows a superior filmcoverage comparing to the NiO layer shown in FIG. 5 , which may resultin a better electronic performance. In this embodiment, the formulationof the NiO precursor ink may comprise 0.87 M nickel nitrate hexahydrate,0.12 M nickel acetate tetrahydrate, 200 mol % ethanolamine, and 464 mol% water in ethylene glycol, where the mole percentage of ethanolamine,and water are relative to Ni moles.

FIGS. 12 to 14 illustrate a UV-Vis absorptance diagram, aphotoluminescence (PL) diagram and a Fourier-transform infraredspectroscopy (FTIR) diagram, respectively, of various NiO layersproduced by the methods and compositions disclosed herein inphotovoltaic devices, in accordance with certain embodiments. Thesevarious layers are referred to as sample numbers 13 to 18, and thecomposition of each NiO layer for each sample is described in greaterdetail below. Sample numbers 16, 17, and 18 further include a 350 nmlayer of FAPbI₃. FIG. 15 illustrates a stylized diagram of an examplethin film stack for sample numbers 13 to 15, in accordance with certainembodiments. FIG. 16 illustrates a stylized diagram of an example filmstack for sample numbers 16 to 18, in accordance with certainembodiments. In some embodiments, the thin film stack with the NiO layershown in FIG. 15 may comprise a substrate, an interfacial layer, and anNiO layer prepared and deposited by the methods described herein. Insome embodiments, the thin film stack with the NiO layer shown in FIG.16 may comprise a substrate, an interfacial layer, and an NiO layerprepared and deposited by the methods described herein, and a layer ofperovskite material. The substrate may be an ITO-coated glass. Theinterfacial layer may be an Al₂O₃ layer. The perovskite material may beFAPbI₃.

The formulation of the NiO precursor ink used to produce the NiO layerin sample number in sample numbers 13-17 included 0.72 M nickel nitratehexahydrate and 0.1-110 mM nickel acetate tetrahydrate in a mixedsolvent of ethylene glycol, ethanolamine, and water having a volumeratio of 12:1.46:1, with additional copper acetate added to obtain thefinal copper and acetate concentrations as described below for eachsample. The formulation of the NiO precursor ink used to produce the NiOlayer in 0sample number 13 includes 5 mol % Cu and 5 mol % acetate. Theformulation of the NiO precursor ink used to produce the NiO layer insample number 14 includes 0 mol % Cu and 12.5 mol % acetate. Theformulation of the NiO precursor ink used to produce the NiO layer insample number 15 includes 5 mol % Cu and 12.5 mol % acetate. Theformulation of the NiO precursor ink used to produce the NiO layer insample number 16 includes 5 mol % Cu and 5 mol % acetate. Theformulation of the NiO precursor ink used to produce the NiO layer insample number 17 includes 0 mol % Cu and 12.5 mol % acetate. Theformulation of the NiO precursor ink used to produce the NiO layer insample number 18 includes 5 mol % Cu and 12.5 mol % acetate. In each ofthe above described samples, the mole percentage of Cu is shown relativeto the total combined moles of Cu and Ni. The mole percentage of acetateis shown relative to the total combined moles of acetate and nickel.

Some or all of materials in accordance with some embodiments of thepresent disclosure may also advantageously be used in any organic orother optical, mechanical, or electronic device, with some examplesincluding, but not limited to: batteries, field-effect transistors(FETs), light-emitting diodes (LEDs), non-linear optical devices,memristors, capacitors, rectifiers, and/or rectifying antennas.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered ormodified and all such variations are considered within the scope andspirit of the present invention. In particular, every range of values(of the form, “from about a to about b,” or, equivalently, “fromapproximately a to b,” or, equivalently, “from approximately a-b”)disclosed herein is to be understood as referring to the power set (theset of all subsets) of the respective range of values, and set forthevery range encompassed within the broader range of values. Also, theterms in the claims have their plain, ordinary meaning unless otherwiseexplicitly and clearly defined by the patentee.

What is claimed is:
 1. A method for depositing a nickel oxide layercomprising: preparing a substrate; depositing a nickel oxide precursorink onto the substrate, wherein the nickel oxide precursor inkcomprises: a solvent comprising diols, alcohol amines, and water;Ni(NO₃)₂·6H₂O; and at least one metal acetate selected from the groupconsisting of Ni(CH₃CO₂)₂·4H₂O and Cu(CH₃CO₂)₂·1H₂O; annealing thenickel oxide precursor ink at a temperature between 250° to 400° Celsiusfor between 10 minutes and 6 hours; and cooling the nickel oxideprecursor ink to form the nickel oxide layer.
 2. The method of claim 1,wherein: the solvent comprises ethylene glycol, ethanolamine and water.3. The method of claim 1, wherein the substrate is selected from thegroup consisting of glass, p-doped silicon, n-doped silicon, sapphire,magnesium oxide, mica, polymers, ceramics, fabrics, wood, drywall,metal, ITO-coated glass, FTO-coated glass, or combinations thereof. 4.The method of claim 1, wherein the substrate is coated with a conductivematerial selected from the group consisting of group consisting ofindium-doped tin oxide (ITO), fluorine-doped tin oxide (FTO), cadmiumoxide (CdO), zinc indium tin oxide (ZITO), aluminum zinc oxide (AZO),aluminum (Al), gold (Au), calcium (Ca), magnesium (Mg), titanium (Ti),steel, chromium (Cr), copper (Cu), silver (Ag), nickel (Ni), tungsten(W), molybdenum (Mo), carbon, and combinations thereof.
 5. The method ofclaim 1, wherein the method is performed under an environment having ahumidity between 10% and 50% and a temperature between 20° and 60°Celsius.
 6. The method of claim 1, wherein the annealing takes place ata temperature of 310° Celsius for a time period of two hours.